Index: wp-includes/comment-template.php
===================================================================
--- wp-includes/comment-template.php	(revision 20291)
+++ wp-includes/comment-template.php	(working copy)
@@ -1533,6 +1533,7 @@
 	$required_text = sprintf( ' ' . __('Required fields are marked %s'), '<span class="required">*</span>' );
 	$defaults = array(
 		'fields'               => apply_filters( 'comment_form_default_fields', $fields ),
+		'form_attributes'			 => apply_filters( 'comment_form_attributes', array() );
 		'comment_field'        => '<p class="comment-form-comment"><label for="comment">' . _x( 'Comment', 'noun' ) . '</label><textarea id="comment" name="comment" cols="45" rows="8" aria-required="true"></textarea></p>',
 		'must_log_in'          => '<p class="must-log-in">' . sprintf( __( 'You must be <a href="%s">logged in</a> to post a comment.' ), wp_login_url( apply_filters( 'the_permalink', get_permalink( $post_id ) ) ) ) . '</p>',
 		'logged_in_as'         => '<p class="logged-in-as">' . sprintf( __( 'Logged in as <a href="%1$s">%2$s</a>. <a href="%3$s" title="Log out of this account">Log out?</a>' ), admin_url( 'profile.php' ), $user_identity, wp_logout_url( apply_filters( 'the_permalink', get_permalink( $post_id ) ) ) ) . '</p>',
@@ -1548,6 +1549,11 @@
 
 	$args = wp_parse_args( $args, apply_filters( 'comment_form_defaults', $defaults ) );
 
+	$form_additionaL_attributes = '';
+	foreach ($args['form_attributes'] as $attribute => $value) {
+		$form_additionaL_attributes .= ' '.$attribute.'="'.$value.'"';
+	}
+
 	?>
 		<?php if ( comments_open() ) : ?>
 			<?php do_action( 'comment_form_before' ); ?>
@@ -1557,7 +1563,7 @@
 					<?php echo $args['must_log_in']; ?>
 					<?php do_action( 'comment_form_must_log_in_after' ); ?>
 				<?php else : ?>
-					<form action="<?php echo site_url( '/wp-comments-post.php' ); ?>" method="post" id="<?php echo esc_attr( $args['id_form'] ); ?>">
+					<?php echo apply_filters('comment_form_element', '<form action="'.site_url( '/wp-comments-post.php' ).'" method="post" id="'.esc_attr( $args['id_form'].'"'.$form_additionaL_attributes.'>'; ?>
 						<?php do_action( 'comment_form_top' ); ?>
 						<?php if ( is_user_logged_in() ) : ?>
 							<?php echo apply_filters( 'comment_form_logged_in', $args['logged_in_as'], $commenter, $user_identity ); ?>